Maharashtra Board Class 9 Science Chapter 16 Heredity and Variation Solutions

Class 9 Science Chapter 16 Heredity And Variation Question Answer Maharashtra Board

 

Question 1. Complete the following sentences by choosing the appropriate words from the brackets.
(Inheritance, sexual reproduction, asexual reproduction, chromosomes, DNA, RNA, gene)
a. Hereditary characters are transferred from parents to offsprings by heredity.
b. Organisms produced by asexual reproduction show minor variations.
c. The component which is in the nuclei of cells and carries the hereditary characteristics is called chromosomes.
d. Chromosomes are mainly made up of DNA, hence they are said to be structural and functional units of gene.
e. Organisms produced through sexual reproduction show major variations.
Answer:
a. Inheritance
b. asexual reproduction
c. chromosomes
d. DNA, gene
e. sexual reproduction
In simple words: This question tests basic terminology related to genetics and heredity, differentiating between types of reproduction and the components of genetic material.

🎯 Exam Tip: Accurately identifying key terms and their definitions is crucial. Pay attention to distinguishing between similar concepts like DNA and genes, and sexual vs. asexual reproduction variations.

 

Question 2. Explain the following.
a. Explain Mendel's monohybrid progeny with the help of any one cross.
Answer:
• Mendel brought about a cross between two pea plants with only pair of contrasting characters. This type of cross is called a monohybrid cross.
• Tall pea plants and dwarf pea plants were used in this cross. Hence this is parent generation (P1).

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र मेंडल के एकल संकर क्रॉस के प्रयोग को दर्शाता है। इसमें पैतृक पीढ़ी (P1) में लंबे (Tall) और बौने (Dwarf) मटर के पौधों के बीच क्रॉस दिखाया गया है, जिसके परिणामस्वरूप पहली संतानी पीढ़ी (F1) में सभी पौधे लंबे (Tall) होते हैं, लेकिन उनका जीनोटाइप हेटेरोजाइगस (Tt) होता है।

Mendel's experiment of the Monohybrid Cross
Parental Generation (P1)
Phenotype:	Tall	Dwarf
Genotype:	TT	tt
Gametes:	T	t
First Filial Generation (F1)
Genotype:	Tt
Phenotype:	Tall
Parental Generation (P2) Selfing in F1
Phenotype:	Tall	Tall
Genotype:	Tt	Tt
Gametes:	T and t	T and t

Second Filial Generation (F2)

	Male gamete
	T	t
Female gamete	T	TT (Tall)	Tt (Tall)
	t	Tt (Tall)	tt (Dwarf)

• All the plants produced in F1 genration are tall, having genotype Tt. This indicates that the gene responsible for tallness in pea plants is dominant over the gene responsible for dwarfness.
• When F1 plants are self pollinated they produce second filial generation (F2).
• In F2 generation both tall and dwarf plants appeared in the ratio 3:1.
• Thus, the genotypic ratio of F2 generation is 3 (Tall) : 1 (Dwarf) and the genotypic ratio is 1 TT : 2 Tt: 1 tt.
In simple words: Mendel's monohybrid cross demonstrates the inheritance of a single trait by crossing purebred tall and dwarf pea plants, showing that the F1 generation is all tall (dominant trait) and the F2 generation exhibits a 3:1 phenotypic ratio (tall:dwarf) and a 1:2:1 genotypic ratio (TT:Tt:tt).

🎯 Exam Tip: When explaining genetic crosses, clearly state the parental genotypes, phenotypes, gametes, and the resulting F1 and F2 generations with their respective phenotypic and genotypic ratios. Diagramming the cross (e.g., using a Punnett square) is often essential for full marks.

 

b. Explain Mendel's dihybrid ratio with the help of any one cross.
Answer:
• In dihybrid cross, Mendel considered two pairs of contrasting characters.
• He made a cross between a pea plant producing rounded and yellow couloured seeds and a pea plant with wrinkled and green coloured seeds.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र मेंडल के द्वि संकर क्रॉस के प्रयोग को दर्शाता है, जिसमें दो अलग-अलग लक्षणों (जैसे बीज का आकार और रंग) की विरासत का अध्ययन किया जाता है। पैतृक पीढ़ी में गोल-पीले और झुर्रीदार-हरे बीजों के बीच क्रॉस से शुरू होकर, यह F1 और F2 पीढ़ियों में जीनोटाइप और फेनोटाइप के वितरण को दिखाता है।

Mendel's experiment of the Monohybrid Cross
Parental Generation (P1)
Phenotype:	Rounded-yellow seeds	Wrinkled-green seeds
Genotype:	RRYY	rryy
Gametes:	RY	ry
First Filial Generation (F1)
Genotype:	RrYy
Phenotype:	(Rounded-yellow seeds)
Parental Generation (P2) Selfing in F1
Phenotype:	Rounded-yellow seeds	Rounded-yellow seeds
Genotype:	RrYy	RrYy
Gametes:	RY, Ry, rY, ry	RY, Ry, rY, ry

Second Filial Generation (F2)

	Male gamete
	RY	Ry	rY	ry
Female gamete	RY	RRYY	RRYy	RrYY	RrYy
	Ry	RRYy	RRyy	RrYy	Rryy
	rY	RrYY	RrYy	rrYY	rrYy
	ry	RrYy	Rryy	rrYy	rryy

• All the plants produced in F1 generation had rounded yellow seeds. This is because in pea plants, round shape of seed is dominant over wrinkled shape and yellow colour of seed is dominant over green colour.
• When F1 plants are self pollinated, they produce four types of gamates – RY, Ry, rY, ry.
• F2 plants formed by the fusion of four types of male gametes and four types of female gametes, had phenotypes such as round yellow, wrinkled yellow, round green and wrinkled green.
• Also, F2 generation showed nine different types of genotypes such as RRYY, RRYy, RRyy, RrYY, RrYy, Rryy, rrYY, rrYy, rryy.
• Phenotypic ratio of dihybrid cross is
9 : 3 : 3 : 1
Round Yellow : Wrinkled Yellow : Round Green : Wrinkled Green
• The genotypic ratio of dihybrid cross is
1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1
RRYY : RRYy : Rryy : RrYY : RrYy : Rryy : rrYY : rrYy : rryy
In simple words: Mendel's dihybrid cross investigates the inheritance of two traits simultaneously, typically resulting in an F2 phenotypic ratio of 9:3:3:1, representing four different combinations of the two traits due to independent assortment of genes.

🎯 Exam Tip: For dihybrid crosses, ensure you correctly derive all possible gamete combinations for the F1 generation and then use a Punnett square to systematically determine the F2 genotypes and phenotypes. Remember the law of independent assortment.

 

c. Distinguish between monohybrid and dihybrid cross.
Answer:

Monohybrid cross	Dihybrid cross
(i) Cross involving a single pair of contrasting characters is called monohybrid cross.	(i) Cross involving two pairs of contrasting characters is called a dihybrid cross.
(ii) F1 plants of monohybrid cross produce two types of gametes.	(ii) F1 plants of dihybrid cross produce four types of gametes.
(iii) Monohybrid cross has a phenotypic ratio of 3 : 1 in F2 generation.	(iii) Dihybrid cross has a phenotypic ratio of 9:3:3:1 in F2 generation.

In simple words: A monohybrid cross studies the inheritance of one trait, while a dihybrid cross studies the inheritance of two traits simultaneously, leading to different gamete production and F2 phenotypic ratios.

🎯 Exam Tip: When distinguishing between biological terms, create a clear table format, listing comparative points side-by-side. Focus on the number of traits involved, gamete formation, and resulting F2 ratios.

 

d. Is it right to avoid living with a person suffering from a genetic disorder?
Answer:
• No, it is not right to avoid living with a person suffering from a genetic disorder.
• Genetic disorders are transmitted from parents to offsprings only and they are non-contagious, i.e., they do not spread from one person to another through contact.
In simple words: It is not right to avoid someone with a genetic disorder because these conditions are not contagious; they are inherited and cannot be spread through contact.

🎯 Exam Tip: Emphasize the non-contagious nature of genetic disorders in your explanation. Understanding the difference between infectious and genetic conditions is key.

 

Question 3. Answers the following questions in your own words.
a. What is meant by 'chromosome'. Explain its types.
Answer:
• The structure in the nucleus of cells that carries the hereditary characteristics is called the chromosome.
• It is made up mainly of nucleic acids and proteins.
• Depending upon the position of the centromere, there are four types of chromosomes.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र गुणसूत्र के विभिन्न प्रकारों को उनके सेंट्रोमेयर की स्थिति के आधार पर दर्शाता है: मेटासेंट्रिक (V-आकार, सेंट्रोमेयर बीच में), सब-मेटासेंट्रिक (U-आकार, सेंट्रोमेयर बीच से थोड़ा हटकर), एक्रोसेंट्रिक (J-आकार, सेंट्रोमेयर एक सिरे के पास) और टेलोसेंट्रिक (I-आकार, सेंट्रोमेयर बिल्कुल सिरे पर)।

(a) Metacentric: The centromere is exactly at the mid-point in this chromosome, and therefore, it looks like the English letter 'V'. The arms of this chromosome are equal in length.
(b) Sub-metacentric: The centromere is somewhere near the mid-point in this chromosome which, therefore, looks like the English letter 'U'. One arm is slightly shorter than the other.
(c) Acrocentric: The centromere is near one end of this chromosome which therefore looks like the English letter 'J'. One arm is much smaller than the other.
(d) Telocentric: The centromere is right at the end of this chromosome making the chromosome look like the English letter 'i'. This chromosome consists of only one arm.
In simple words: Chromosomes are thread-like structures in the cell nucleus, made of DNA and proteins, that carry genetic information; their types (metacentric, sub-metacentric, acrocentric, telocentric) are classified by the centromere's position, influencing their shape during cell division.

🎯 Exam Tip: When defining chromosomes, include their composition and function. For types, clearly describe each based on centromere position and its characteristic shape (e.g., V-shaped for metacentric).

 

b. Describe the structure of the DNA molecule.
Answer:

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र DNA की दोहरी हेलिक्स संरचना को दर्शाता है, जिसमें नाइट्रोजनस बेस के जोड़े (एडेनिन, गुआनिन, साइटोसिन, थायमिन) एक-दूसरे से जुड़े हुए सीढ़ी के डंडों की तरह दिखते हैं। शुगर और फॉस्फोरिक एसिड के 'रेल' इसकी बैकबोन बनाते हैं, और चित्र 3.4 nm की पूर्ण हेलिक्स मोड़ और 0.34 nm के बेस जोड़ी अंतर को दर्शाता है।

• In 1953, Watson and Crick proposed a model of the DNA molecule.
• As per their model, two parallel threads (strands) of nucleotides are coiled around each other to form a double helix structure. This structure can be compared with a coiled and a flexible ladder.
• Each strand of DNA is made up of many small molecules known as nucleotides.
• Each nucleotide is made up of a molecule of nitrogen base and phosphoric acid joined to a molecule of sugar.
• There are four types of nitrogen bases-adenine, guanine, cytosine and thymine. Adenine and guanine are called as purines while cytosine and thymine are called as pyrimidines.
• Nucleotides are arranged like a chain in the DNA.
• The two threads (strands) of the DNA are comparable to the two rails of the ladder and each rail is made up of alternately joined molecules of sugar and phosphoric acid.
• Each rung of the ladder is a pair of nitrogenous bases joined by hydrogen bonds. Adenine always pairs with thymine and cytosine always pairs with guanine.
In simple words: DNA is a double helix molecule resembling a twisted ladder, composed of two nucleotide strands. Each nucleotide contains a sugar, a phosphate, and a nitrogenous base (adenine, guanine, cytosine, or thymine), with specific base pairing forming the "rungs" of the ladder.

🎯 Exam Tip: When describing DNA structure, include the key components (nucleotides, sugar, phosphate, nitrogenous bases), the double helix model, and the specific base pairing rules (A-T, G-C). Mentioning Watson and Crick is important for historical context.

 

c. Express your opinion about the use of DNA fingerprinting.
Answer:
• DNA fingerprinting is the technique in which the sequence of the genes in the DNA of a person, i.e., the genome of the person is identified.
• This technique is useful to identify the lineage and to identify criminals because it is unique to every person.
• It is also useful to identify paternity and maternity disputes etc.
• This technique was developed by Professor of genetics Sir Alec Jeffreys.
• A common method of collecting a reference sample, is in the use of a buccal swab. If this is not available, blood or saliva or hair sample may be used.
• Just like your actual fingerprint, your DNA fingerprint is something that you are born with. It is unique to you.
• DNA fingerprint is very useful in forensic science.
In simple words: DNA fingerprinting is a powerful forensic tool that identifies individuals by their unique genetic sequences, proving invaluable in crime investigations, paternity disputes, and establishing lineage.

🎯 Exam Tip: Focus on the uniqueness of an individual's DNA profile and its practical applications, especially in forensic science and resolving familial relationships. Mention the non-invasive methods of sample collection.

 

d. Explain the structure, function and types of RNA.
Answer:
• Ribonucleic acid (RNA) is an important nucleic acid of the cell.
• RNA is made up of ribose sugar, phosphate molecules and four types of nitrogenous bases adenine, guanine, cytosine and uracil.
• The nucleotide i.e., smallest unit of the chain of the RNA molecule is formed by the combination of a ribose sugar, phosphate molecule and one of the nitrogen bases.
• Large numbers of nucleotides are bonded together to form the macromolecule of RNA.
• RNA performs the function of protein synthesis.
• According to function, there are three types of RNA:
(a) Ribosomal RNA (rRNA): It is the component of cellular organelle ribosome. Ribosomes perform the function of protein synthesis.
(b) Messenger RNA (mRNA): It carries the information for protein synthesis from genes (i.e. DNA segment in the cell nucleus) to ribosomes (in the cytoplasm) which produce the proteins.
(c) Transfer RNA (tRNA): It carries the amino acid up to the ribosomes as per the message of the mRNA.
In simple words: RNA, a single-stranded nucleic acid, consists of ribose sugar, phosphate, and nitrogenous bases (adenine, guanine, cytosine, uracil); it is crucial for protein synthesis, with its three main types-mRNA, tRNA, and rRNA-playing distinct roles in carrying genetic messages, transporting amino acids, and forming ribosomes, respectively.

🎯 Exam Tip: When explaining RNA, highlight its single-stranded nature and the presence of uracil instead of thymine. Clearly define the roles of mRNA, tRNA, and rRNA in the process of protein synthesis.

 

e. Why is it necessary for people to have their blood examined before marriage?
Answer:
• If people have their blood examined before marriage, the partners will know about the possible genetic diseases that their children might inherit. So they may decide not to have children or not to get married.
• Blood tests before marriage are also done to check for any contagious disease in the partners. This will help to protect the partners from contagious diseases like STDs.
In simple words: Pre-marital blood examination is essential to identify potential hereditary diseases that could be passed to offspring, allowing informed family planning, and also to screen for contagious diseases like STDs to protect the partners' health.

🎯 Exam Tip: Emphasize both genetic inheritance risks and the prevention of contagious diseases as primary reasons for pre-marital blood tests. Highlight the importance of informed decision-making regarding family planning and health.

 

Question 4. Write a brief note on each.
a. Down syndrome
Answer:
• Down syndrome is the disorder arising due to chromosomal abnormality.
• This is the first discovered and described the chromosomal disorder in human beings.
• This disorder is characterized by the presence of 47 chromosomes. It is described as the trisomy of the 21st pair.
• Infants with this disorder have one extra chromosome with the 21st pair in every cell of the body. Therefore, they have 47 chromosomes instead of 46.
• Children suffering from Down syndrome are usually mentally retarded and have a short lifespan. Mental retardation is the most prominent characteristic.
• Other symptoms include short height, short wide neck, flat nose, short fingers, scanty hair, single horizontal crease on palm and a life expectancy of about 16-20 years.
In simple words: Down syndrome is a genetic disorder caused by trisomy 21 (an extra copy of chromosome 21), leading to 47 chromosomes instead of 46, and is characterized by mental retardation, short stature, and distinct physical features.

🎯 Exam Tip: For Down syndrome, focus on the cause (Trisomy 21), the chromosome count (47), and the key distinguishing symptoms like mental retardation and specific physical traits.

 

b. Monogenic disorders
Answer:
• Disorders occurring due to mutation in any single gene into a defective one are called monogenic disorders.
• Approximately 4000 disorders of this type are now known.
• Due to abnormal genes, their products are either produced in insufficient quantity or not produced at all.
• It causes abnormal metabolism and may lead to death at a tender age.
• Examples of monogenic disorders are Hutchinson's disease, Tay-Sachs disease, galactosaemia, phenylketonuria, sickle cell anaemia, cystic fibrosis, albinism, haemophilia, night blindness etc.
In simple words: Monogenic disorders are genetic conditions caused by a mutation in a single gene, leading to defective or insufficient gene products, abnormal metabolism, and often severe health consequences, with examples including sickle cell anaemia and haemophilia.

🎯 Exam Tip: Define monogenic disorders by their cause (single gene mutation). Provide a few clear examples, as these are often asked in tests. Briefly mention the consequence of abnormal gene products.

 

c. Sickle cell anaemia: symptoms and treatment.
Answer:
• Sickle-cell anaemia is a hereditary disease caused due to mutation in a single gene. It is a monogenic disorder.
• Normal haemoglobin has glutamic acid as the 6th amino acid in its molecular structure. However, if it is replaced by valine, the shape/structure of the haemoglobin molecule, changes.
• Due to this, the erythrocytes (RBCs) which are normally biconcave become sickle-shaped. This condition is called sickle-cell anaemia. The oxygen-carrying capacity of haemoglobin in such individuals is very low.
• In this condition, clumping and thereby, destruction of erythrocytes occurs most often. As a result, blood vessels are obstructed and the circulatory system, brain, lungs, kidneys, etc. are damaged.
• Symptoms of sickle-cell anaemia are swelling of legs and hands, pain in joints, severe general body aches, frequent cold and cough, constant low-grade fever, exhaustion, pale face, low haemoglobin count.
• A person suffering from sickle-cell anaemia should take a tablet of folic acid daily.
In simple words: Sickle cell anaemia is a monogenic hereditary disease where a single gene mutation causes normal red blood cells to become sickle-shaped, leading to poor oxygen transport, vessel blockage, and symptoms like pain, swelling, and low hemoglobin; daily folic acid is a common part of management.

🎯 Exam Tip: Detail the genetic cause (single gene mutation, amino acid change), the impact on red blood cell shape and function, and list prominent symptoms. Mention a key treatment like folic acid supplements.

 

Question 5. How are the items in groups A, B and C inter-releated?
Answer: This question lacks the groups A, B, and C in the provided text, hence a direct answer cannot be formed based on the input.
In simple words: (Answer could not be provided as the groups A, B, and C for inter-relationship analysis were missing from the question.)

🎯 Exam Tip: Always read the question carefully to ensure all necessary information (like groups A, B, C) is present before attempting to answer. If information is missing, state it clearly.

 

Question 6. Filling the blanks based on the given relationship.
a. 44 + X : Turner syndrome : : 44 + XXY: -
b. 3:1 Monohybrid : : 9:3:3:1 :
c. Women : Turner syndrome :: Men :
Answer:
a. Klinefelter syndrome
b. Dihybrid
c. Klinefelter syndrome
In simple words: This question tests your knowledge of genetic syndromes and Mendelian ratios by asking you to complete analogies based on known genetic conditions and inheritance patterns.

🎯 Exam Tip: For analogy questions, identify the relationship between the first pair and apply the same relationship to the second pair. Knowing chromosomal abnormalities and standard genetic ratios is essential.

 

Question 7. Complete the tree diagram below based on types of hereditary disorders.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख वंशानुगत विकारों के प्रकारों को एक ट्री डायग्राम के रूप में दर्शाता है। इसमें मुख्य रूप से चार श्रेणियों को दिखाया गया है: क्रोमोसोमल असामान्यताएं (Chromosomal Abnormalities), मोनोजेनिक विकार (Monogenic Disorders), माइटोकॉन्ड्रियल विकार (Mitochondrial disorder), और पॉलीजेनिक विकार (Polygenic Disorders)। प्रत्येक श्रेणी के तहत विशिष्ट विकारों के उदाहरणों को सूचीबद्ध किया गया है।

Answer:

Chromosomal Abnormalities	Monogenic Disorders	Mitochondrial disorder	Polygenic Disorders
Down syndrome, Turner syndrome, Klinefelter syndrome.	Albinism, sickle cell anaemia, phenylketonuria, Hutchinson's disease, Tay-Sachs disease, galactosaemia, cystic fibrosis, haemophilia, night blindness.	Leber hereditary optic neuropathy.	Spina bifida (defect of spinal cord), diabetes, blood pressure, heart disorders, asthma obesity, cleft lip, cleft palate constricted stomach.

In simple words: Hereditary disorders are broadly classified into chromosomal abnormalities, monogenic disorders (single gene mutations), mitochondrial disorders, and polygenic disorders (multiple genes and environmental factors), each having distinct causes and examples.

🎯 Exam Tip: To complete such diagrams or tables, ensure you categorize each disorder correctly based on its genetic origin (chromosome, single gene, mitochondria, multiple genes) and list relevant examples for each category.

 

Question 1. How do specific traits or characteristics appear in organisms?
Answer:
• Information necessary for synthesis of a particular protein is stored in the DNA.
• The segment of DNA which contains all the information for synthesis of a particular protein is called a gene for that protein.
• To understand how a specific trait is expressed, let us consider plant height as an example.
• We know that there are growth hormones in plants. Increase in the height of plants depends upon the quantity of growth hormones.
• The quantity of growth hormone produced by a plant depends upon the efficiency of the concerned enzyme.
• Efficient enzymes produce a greater quantity of the hormone due to which the height of the plant increases.
• However, if the enzymes are less efficient, a smaller quantity of hormone is produced leading to the stunting of the plant.
• Thus, the expression of traits is controlled by the genes.
In simple words: Specific traits appear in organisms because genes, which are segments of DNA, contain the instructions for synthesizing proteins; these proteins, often enzymes, regulate biochemical processes like hormone production, ultimately determining the expression of a characteristic.

🎯 Exam Tip: Explain the gene-protein-trait pathway. Use a clear example like plant height to illustrate how gene efficiency impacts enzyme production, which in turn affects the observable characteristic.

 

Question 2. Show the monohybrid cross between (RR) and (rr) and write the phenotypic and genotypic ratio of F2 generation.
Answer:
Parental Generation (P1)
Phenotype: Round Seeds Wrinkled Seeds
Genotype RR rr
Gametes R r

First Filial Generation (F1)
Rr
Phenotype: Round Seeds

Parental Generation (P2) Selfing in F1
Phenotype: Round Seeds Round Seeds
Genotype: Rr Rr
Gametes: R and r R and r

Second Filial Generation (F2)

	Male gamete
	R	r
Female gamete	R	RR (Round)	Rr (Round)
	r	Rr (Round)	rr (Wrinkled)

Phenotypic ratio : 3 Round : 1 Wrinkled
Genotypic ratio : 1 RR : 2 Rr : 1 rr
In simple words: A monohybrid cross between pure round (RR) and pure wrinkled (rr) seeds results in all round (Rr) seeds in the F1 generation. Self-pollination of F1 yields an F2 generation with a phenotypic ratio of 3 Round:1 Wrinkled and a genotypic ratio of 1 RR:2 Rr:1 rr.

🎯 Exam Tip: When illustrating a monohybrid cross, clearly label each generation (P1, F1, F2), their genotypes, phenotypes, and gametes. The Punnett square is essential for visually representing the F2 generation and accurately deriving its ratios.

 

Question 3. Why did the characteristic of the Rounded- Yellow seeds alone appear in the F1 generation but not the characteristic of the wrinkled- green seeds?
Answer:
• Rounded-Yellow seeds is a dominant characteristic whereas wrinkled-green seeds is a recessive characteristic.
• Therefore only the characteristic of Rounded- Yellow seeds appeared in the F1 generation.
In simple words: The characteristic of rounded-yellow seeds appeared in the F1 generation because it is a dominant trait, while wrinkled-green seeds are a recessive trait and thus their phenotype was masked in the F1 generation by the presence of the dominant alleles.

🎯 Exam Tip: This question directly tests the concept of dominance and recessiveness. Ensure your answer clearly states that the dominant trait expresses itself in the F1 generation, masking the recessive trait.

 

Question 4. Do all boys and girls of your class look alike?
Answer:
• No, all the boys and girls of my class do not look alike.
• There is a lot of variation among them.
In simple words: No, individuals even within the same class do not look exactly alike because genetic variations and environmental factors contribute to diverse physical appearances among humans.

🎯 Exam Tip: This question is about observable variation. Connect the observation (not looking alike) to the underlying biological principle of genetic variation, which is a fundamental concept in heredity.

 

Question 5. Carefully observe your classmate's earlobes.
Answer:
• Most of the classmates have free earlobes while very few have attached ear lobes.
• This shows that in humans free earlobes is a dominant characteristic whereas attached earlobe is a recessive characteristic.
In simple words: Observation of classmates' earlobes reveals that most have free earlobes, indicating it is a dominant trait, while fewer have attached earlobes, which is a recessive trait in humans.

🎯 Exam Tip: Use the observation to illustrate the concept of dominant and recessive traits in human genetics. Clearly state which phenotype corresponds to the dominant characteristic and which to the recessive.

 

Question 6. Irrespective of all of us being humans, what difference do you notice in our skin colour?
Answer:
• Irrespective of all of us being humans, there is a lot of variation in our skin colour. Some people are light-skinned while some are dark-skinned.
• The difference in skin colour is due to the gene responsible for the production of the pigment melanin.
In simple words: Despite being human, individuals exhibit varied skin colors, ranging from light to dark, primarily due to the genetic control over the production of the pigment melanin.

🎯 Exam Tip: Link variations in observable human traits like skin color to the genetic control of specific biological processes, such as melanin production, reinforcing the role of genes in phenotype.

 

Question 7. All of you are in std. IX. Why then are some students tall and some short?
Answer:
Our height is decided by gene. People who are tall have genes for tallness whereas people who are short have genes for shortness and hence the variation.
In simple words: Differences in height among students are due to genetic variations; individuals inherit genes that determine potential for tallness or shortness, leading to observable variations in height.

🎯 Exam Tip: Directly attribute height variation to genetic inheritance. Mention that genes determine the potential for traits, explaining why even within the same age group, significant differences can exist.

 

Choose And Write The Correct Option:

 

Question 1. The similarities and differences are all the effect of
(a) Heredity
(b) Fertilization
(c) Evolution
(d) Natural selection
Answer: (a) Heredity
In simple words: Heredity is the passing of traits from parents to offspring, which explains both the similarities (shared traits) and differences (variations in inherited traits) seen among individuals.

🎯 Exam Tip: Understand that heredity is the fundamental process responsible for the transmission of traits, encompassing both resemblances and variations within a species.

 

Question 2. Each chromosome appears midway during cell division.
(a) Circular
(b) Rod-shaped
(c) Dumbbell-shaped
(d) Bottle-shaped
Answer: (c) dumbbell-shaped
In simple words: During cell division, particularly metaphase, chromosomes condense and become visible, often appearing in a characteristic dumbbell-shape before splitting.

🎯 Exam Tip: Recall the different phases of cell division and the appearance of chromosomes during each phase. The condensed, replicated chromosome often takes on a dumbbell-like form.

 

Question 3. The chromosome in which the centromere is exactly at the mid-point is called chromosome.
(a) sub-metacentric
(b) metacentric
(c) acrocentric
(d) telocentric
Answer: (b) metacentric
In simple words: A metacentric chromosome is characterized by its centromere being located precisely in the middle, resulting in arms of equal length and a V-shape during anaphase.

🎯 Exam Tip: Memorize the classification of chromosomes based on centromere position. "Metacentric" refers to the centromere being centrally located.

 

Question 4. The chromosome in which the centromere is somewhere near the mid-point is called chromosome.
(a) metacentric
(b) acrocentric
(c) sub-metacentric
(d) telocentric

Question 5.
The chromosome in which the centromere is near one end of the chromosome is called chromosome.
(a) metacentric
(b) acrocentric
(c) sub-metacentric
(d) telocentric
Answer: (d) telocentric
In simple words: A telocentric chromosome has its centromere located at the very end, giving it a characteristic "i" shape.

🎯 Exam Tip: Remember the different classifications of chromosomes based on centromere position for quick identification in exams.

Question 6.
Sex chromosomes are called
(a) homologous chromosomes
(b) autosomes
(c) allosomes
(d) metacentric chromosomes
Answer: (c) allosomes
In simple words: Allosomes are the sex chromosomes (X and Y in humans) that determine the sex of an individual, distinguishing them from autosomes.

🎯 Exam Tip: Knowing the correct terminology for different types of chromosomes is crucial for genetics questions.

Question 7.
Which of the following is absent in RNA?
(a) Adenine
(b) Uracil
(c) Cytosine
(d) Thymine
Answer: (d) Thymine
In simple words: RNA uses uracil (U) instead of thymine (T) as one of its nitrogenous bases, while DNA contains thymine.

🎯 Exam Tip: Distinguish between the nitrogenous bases present in DNA and RNA, as this is a fundamental difference.

Question 8.
DNA was discovered by
(a) Watson and Crick
(b) Frederick Miescher
(c) Gregor Johann Mendel
(d) Robert Brown
Answer: (b) Frederick Miescher
In simple words: Frederick Miescher first isolated nucleic acids, including DNA, from the nuclei of white blood cells in 1869.

🎯 Exam Tip: Accurately recall the scientists associated with key discoveries in genetics, such as DNA's initial isolation versus its double helix model.

Question 9.
The double helix model of DNA was produced by
(a) Watson and Crick
(b) Frederick Miescher
(c) Gregor Johann Mendel
(d) Robert Hooke
Answer: (a) Watson and Crick
In simple words: Watson and Crick proposed the iconic double helix structure of DNA, which explains how genetic information is stored and replicated.

🎯 Exam Tip: Remember the specific contributions of scientists; Miescher discovered DNA, while Watson and Crick elucidated its structure.

Question 10.
The molecule of RNA which is a component of the ribosome organelle is called a
(a) mRNA
(b) tRNA
(c) rRNA
(d) DNA
Answer: (c) rRNA
In simple words: Ribosomal RNA (rRNA) is a structural and catalytic component of ribosomes, essential for protein synthesis.

🎯 Exam Tip: Understand the different types of RNA (mRNA, tRNA, rRNA) and their specific roles in protein synthesis.

Question 11.
In a monohybrid cross, the phenotypic ratio of F, generation is
(a) 1 tall: 3 dwarf
(b) 2 tall: 2 dwarf
(c) 3 tall: 1 dwarf
(d) 3 tall: 2 dwarf
Answer: (c) 3 talhl dwarf
In simple words: In a monohybrid cross between two heterozygous parents, the F2 phenotypic ratio for a dominant-recessive trait is typically 3 dominant to 1 recessive.

🎯 Exam Tip: Memorize the standard phenotypic and genotypic ratios for monohybrid and dihybrid crosses, as they are frequently tested.

Question 12.
- arises due to either inheritance of only X chromosome from parents or due to inactivation of the gender-related part of X-chromosomes.
(a) Down syndrome
(b) Turner syndrome
(c) Klinefelter syndrome
(d) Albinism
Answer: (b) Turner syndrome
In simple words: Turner syndrome is a chromosomal disorder in females characterized by the absence of all or part of a second X chromosome, resulting in a 44+X karyotype.

🎯 Exam Tip: Be able to associate specific chromosomal abnormalities and genetic conditions with their defining characteristics.

Question 13.
Progenies of normal man and sufferer woman for sickle-cell anaemia will be
(a) all normal
(b) 25% normal and 75% sufferer
(c) all carrier
(d) all sufferer
Answer: (c) all carrier
In simple words: If a normal man (AA) mates with a sufferer woman (SS), all offspring will be carriers (AS) for sickle-cell anaemia.

🎯 Exam Tip: Practice Punnett squares for genetic crosses to accurately predict the genotypes and phenotypes of offspring, especially for hereditary diseases.

Question 14.
- is a mitochondrial disorder.
(a) Down syndrome
(b) Cleft palate
(c) Spina bifida
(d) Leber hereditary optic neuropathy
Answer: (d) Leber hereditary optic neuropathy
In simple words: Leber hereditary optic neuropathy (LHON) is a genetic condition caused by mutations in mitochondrial DNA, leading to vision loss.

🎯 Exam Tip: Understand that some genetic disorders are specifically linked to mitochondrial DNA and are maternally inherited.

Question 15.
- is a monogenic disorder.
(a) Haemophilia
(b) Cleft palate
(c) Diabetes
(d) Spina bifida
Answer: (a) Haemophilia
In simple words: Haemophilia is a monogenic disorder, meaning it is caused by a mutation in a single gene.

🎯 Exam Tip: Differentiate between monogenic (single gene) and polygenic (multiple genes) disorders, as well as chromosomal abnormalities.

Question 16.
- is a recessive character of pea plant.
(a) Round shape of seeds
(b) White colour of flowers
(c) Green colour of pods
(d) Inflated shape of pods
Answer: (b) White colour of flowers
In simple words: In Mendel's pea plant experiments, white flower color was observed to be a recessive trait compared to purple flowers.

🎯 Exam Tip: Familiarize yourself with Mendel's seven contrasting characters in pea plants and their dominant/recessive forms.

Question 17.
- is a dominant character of pea plant.
(a) Dwarf height
(b) Yellow colour of pod
(c) Yellow colour of seeds
(d) Terminal position of flower
Answer: (c) Yellow colour of seeds
In simple words: Yellow seed color is a dominant trait in pea plants, meaning it will be expressed even if only one copy of the allele is present.

🎯 Exam Tip: Clearly differentiate between dominant and recessive traits in Mendelian genetics, often tested with examples.

Question 18.
- is a dominant character in human beings.
(a) Non-rolling tongue
(b) Attached ear lobe
(c) Absence of hair on arms
(d) Free ear lobe
Answer: (d) Free ear lobe
In simple words: Free ear lobes are a dominant human trait, meaning most individuals will display this phenotype if they inherit at least one dominant allele.

🎯 Exam Tip: Be aware of common human traits that are dominant or recessive, as they serve as practical examples in genetics.

Question 19.
- is a recessive character in human beings.
(a) Absence of hair on arms
(b) Black and curly hair
(c) Free earlobe
(d) Presence of hair on arms
Answer: (a) Absence of hair on arms
In simple words: The absence of hair on arms is considered a recessive human trait, requiring two copies of the recessive allele to be expressed.

🎯 Exam Tip: Understanding human genetic traits (dominant/recessive) helps in applying genetic principles to real-world scenarios.

Question 20.
If one parent is normal and one parent is carrier of sickle-cell anaemia, then the progenies will be
(a) all normal
(b) 50% normal and 50% carrier
(c) 50% carrier and 50% sufferer
(d) all carrier
Answer: (b) 50% normal and 50% carrier
In simple words: If a normal parent (AA) and a carrier parent (AS) mate, half of their offspring will be normal (AA) and half will be carriers (AS).

🎯 Exam Tip: Use Punnett squares for inheritance patterns of recessive genetic disorders to determine the probability of different genotypes in offspring.

Question 21.
If one parent is carrier and one parent is a sufferer of sickle-cell anaemia, then the progenies will be
(a) 50% normal and 50% carrier
(b) all sufferers
(c) 50% carrier and 50% sufferer
(d) all carrier
Answer: (c) 50% carrier and 50% sufferer
In simple words: When a carrier (AS) and a sufferer (SS) parent mate, 50% of their children will be carriers (AS) and 50% will be sufferers (SS) of sickle-cell anaemia.

🎯 Exam Tip: Always draw Punnett squares to visualize the possible combinations and accurately calculate the ratios of offspring for complex inheritance problems.

Find The Odd Man Out:

Question 1.
Adenine, thymine, cytosine, uracil
Answer: Adenine. It is a purine whereas the others are pyrimidines.
In simple words: Adenine is a purine (a double-ring nitrogenous base), while thymine, cytosine, and uracil are pyrimidines (single-ring nitrogenous bases).

🎯 Exam Tip: Categorize nitrogenous bases as purines (Adenine, Guanine) and pyrimidines (Cytosine, Thymine, Uracil) to quickly identify the odd one out based on structure.

Question 2.
Axillary flower, green pod, green seed, inflated pod
Answer: Green seed. It is a recessive character of pea plant whereas the others are dominant characters.
In simple words: Green seed color is a recessive trait in pea plants, while axillary flower position, green pod color, and inflated pod shape are all dominant traits.

🎯 Exam Tip: Knowing Mendel's dominant and recessive traits for pea plants is essential for "odd one out" questions based on inheritance patterns.

Question 3.
Constricted pod, purple flower, axillary flower, yellow seeds.
Answer: Constricted pod. It is a recessive character of pea plant whereas the others are dominant characters.
In simple words: Constricted pod shape is a recessive trait in pea plants, whereas purple flower color, axillary flower position, and yellow seed color are all dominant traits.

🎯 Exam Tip: Be precise in recalling which specific traits are dominant and which are recessive to avoid errors in character classification.

Question 4.
Green seeds, wrinkled seeds, terminal flower, green pod.
Answer: Green pod. It is a dominant character of pea plant whereas the others are recessive characters.
In simple words: Green pod is a dominant trait in pea plants, while green seeds, wrinkled seeds, and terminal flower position are all recessive traits.

🎯 Exam Tip: Pay close attention to the specific wording of traits (e.g., "green seeds" vs. "green pod") as their dominance can differ.

Question 5.
Attached ear lobes, brown and straight hair, non-rolling tongue, presence of hair on arms.
Answer: Presence of hair on arms. It is a dominant characteristic of human beings whereas the others are recessive characters.
In simple words: The presence of hair on arms is a dominant human trait, while attached ear lobes, brown and straight hair (relative to black and curly), and non-rolling tongue are recessive traits.

🎯 Exam Tip: When dealing with human traits, remember to consider common examples of dominant and recessive characteristics.

Question 6.
Cystic fibrosis, albinism, spina bifida, sicklecell anaemia.
Answer: Spina bifida. It is a polygenic disorder whereas the others are monogenic disorders.
In simple words: Spina bifida is a polygenic disorder (influenced by multiple genes and environmental factors), while cystic fibrosis, albinism, and sickle-cell anaemia are monogenic disorders (caused by a single gene defect).

🎯 Exam Tip: Classify genetic disorders by their underlying cause (monogenic, polygenic, chromosomal) for accurate identification.

Question 7.
Fiutchinson's disease, phenylketonuria, nightblindness, leber hereditary optic neuropathy.
Answer: Leber hereditary optic neuropathy. It is a mitochondrial disorder whereas the others are monogenic disorders.
In simple words: Leber hereditary optic neuropathy is a mitochondrial disorder, meaning it results from mutations in mitochondrial DNA, while the other conditions listed are monogenic disorders.

🎯 Exam Tip: Highlight unique inheritance patterns like mitochondrial inheritance to distinguish disorders that don't follow typical Mendelian rules.

Complete The Analogy:

Question a.
Tall plant: Phenotype :: Tt:
Answer: Genotype
In simple words: Phenotype refers to the observable characteristics (like a tall plant), while genotype refers to the genetic makeup (like Tt).

🎯 Exam Tip: Clearly define phenotype as observable traits and genotype as the underlying genetic code for clarity.

Question b.
Dominant trait : Axial position of flower :: Recessive trait:
Answer: Terminal position of flower
In simple words: Axial flower position is a dominant trait in pea plants, and its contrasting recessive trait is terminal flower position.

🎯 Exam Tip: Match dominant traits with their corresponding recessive counterparts to understand Mendelian inheritance.

Question c.
Women: 44 + XX :: Men :
Answer: 44 + XY
In simple words: The normal human female karyotype is 44 autosomes plus XX sex chromosomes, while the normal male karyotype is 44 autosomes plus XY sex chromosomes.

🎯 Exam Tip: Know the standard human karyotypes for males and females (autosomes + sex chromosomes).

Question d.
Adenine and Guanine : Purine :: Cytosine and Thymine :
Answer: Pyrimidine
In simple words: Adenine and Guanine are classified as purines due to their double-ring structure, while Cytosine and Thymine are pyrimidines, characterized by a single-ring structure.

🎯 Exam Tip: Classify nitrogenous bases into purines and pyrimidines, a fundamental concept in nucleic acid structure.

Match The Columns

Question 1.

Column 1	Column 2	Column 3
(1) Leber hereditary optic neuropathy	(a) 44 + XXY	(i) Pale skin, white hairs.
(2) Diabetes	(b) 45 + X	(ii) Men are sterile.
(3) Albinism	(c) Mitochondrial disorder	(iii) Women are sterile.
(4) Turner syndrome	(d) Polygenic disorder	(iv) This disorder arises during development of zygote.
(5) Klinefelter Syndrome	(e) Monogenic disorder	(v) Effect on blood- glucose level.

Answer:
(1 - c - iv),
(2 - d - v),
(3 - e - i),
(4-b- iii),
(5 - a - ii)
In simple words: This matching exercise connects genetic disorders with their types and characteristics, such as Leber hereditary optic neuropathy being a mitochondrial disorder affecting zygote development, and Albinism being a monogenic disorder causing pale skin.

🎯 Exam Tip: Practice linking genetic disorders with their classifications (monogenic, polygenic, chromosomal, mitochondrial) and key symptoms for comprehensive understanding.

Question 2.

Column 'A'	Column 'B'
(1) Yellow and rinkled	(a) yyrr
(2) Green and round	(b) YyRr
(3) Yellow and round	(c) YYrr
(4) Green and wrinkled	(d) yyRr

Answer:
(1 - c),
(2 - d),
(3 - b),
(4 - a)
In simple words: This matching task correlates phenotypic descriptions of pea plant seeds with their respective genotypes, illustrating how different allele combinations lead to observable traits.

🎯 Exam Tip: Understand how to convert phenotypic descriptions into corresponding genotypes for Mendelian traits, especially using shorthand notation like 'Y' for yellow and 'r' for wrinkled.

Question 3.

Column 'A'	Column 'B'
(1) Tay-Sachs disease	(a) Multifactorial disorder
(2) Diabetes	(b) Destruction of erythrocytes
(3) Sickle-cell anaemia	(c) Absence of melanin
(4) Albinism	(d) Monogenic disorder

Answer:
(1 - d),
(2 - a),
(3 - b),
(4 - c)
In simple words: This matching exercise pairs genetic disorders with their classifications or key symptoms, such as Tay-Sachs being monogenic and diabetes being multifactorial.

🎯 Exam Tip: Focus on understanding the primary cause or characteristic symptom of common genetic disorders to successfully match them.

State Whether The Following Statements Are True Or False. Correct The False Statement:

Question 1.
Offsprings produced through asexual reproduction show greater variations as compared to those produced through sexual reproduction.
Answer: False. Offsprings produced through asexual reproduction show minor variations as compared to those produced through sexual reproduction.
In simple words: Asexual reproduction produces genetically identical offspring with only minor variations due to mutations, whereas sexual reproduction mixes genetic material from two parents, leading to significant variations.

🎯 Exam Tip: Remember that genetic variation is a hallmark of sexual reproduction, providing evolutionary advantages that asexual reproduction lacks.

Question 2.
Information necessary for protein synthesis is stored in the RNA.
Answer: False. Information necessary for protein synthesis is stored in the DNA.
In simple words: While RNA plays a crucial role in carrying and translating genetic information, the original blueprint and primary storage of genetic information for protein synthesis reside in DNA.

🎯 Exam Tip: Understand the central dogma of molecular biology: DNA stores information, which is transcribed into RNA, and then translated into protein.

Question 3.
The quantity of growth hormone produced by a plant depends upon the efficiency of the concerned enzyme.
Answer: True
In simple words: The amount of growth hormone produced by a plant is directly influenced by how efficiently the enzymes involved in its synthesis function.

🎯 Exam Tip: Connect enzyme efficiency to the regulation of biological processes and the expression of traits, like plant height.

Question 4.
The chromosome in which the centromere is exactly at the mid-point is called telocentric chromosome.
Answer: False. The chromosome in which the centromere is exactly at the mid-point is called metacentric chromosome.
In simple words: A metacentric chromosome has its centromere centrally located, giving it a V-shape during anaphase, unlike a telocentric chromosome where the centromere is at the very end.

🎯 Exam Tip: Differentiate clearly between the types of chromosomes based on centromere position (metacentric, sub-metacentric, acrocentric, telocentric).

Question 5.
RNA molecules are called master molecules.
Answer: False. DNA molecules are called master molecules.
In simple words: DNA is considered the "master molecule" because it contains the complete genetic instructions for an organism, while RNA primarily functions in gene expression and regulation.

🎯 Exam Tip: Reinforce the understanding of DNA as the primary genetic material and controller of cellular activities.

Question 6.
The pair of sex chromosomes are called autosomes.
Answer: False. The pair of sex chromosomes is called allosomes.
In simple words: Sex chromosomes (X and Y) are known as allosomes because they determine an individual's sex, distinguishing them from the non-sex-determining autosomes.

🎯 Exam Tip: Correctly use the terms 'autosomes' for non-sex chromosomes and 'allosomes' (or sex chromosomes) for those determining gender.

Question 7.
In DNA, Adenine always pairs with thymine and cytosine always pairs with guanine.
Answer: True
In simple words: This statement is true, representing Chargaff's rules and the complementary base pairing in DNA: A pairs with T, and C pairs with G.

🎯 Exam Tip: Remember the specific base pairing rules (A-T, C-G) as they are fundamental to DNA structure and function.

Question 8.
In humans there are 23 pairs of autosomes and one pair of allosomes.
Answer: False. In humans, there are 22 pairs of autosomes and one pair of allosomes.
In simple words: Humans have a total of 23 pairs of chromosomes, comprising 22 pairs of autosomes and 1 pair of sex chromosomes (allosomes).

🎯 Exam Tip: Accurately state the number of autosomes and allosomes in human karyotypes.

Question 9.
The phenotypic and genotypic ratios are not same.
Answer: True
In simple words: Phenotypic ratios describe the observable traits, while genotypic ratios describe the genetic makeup, and these are often different due to dominant-recessive relationships where different genotypes can result in the same phenotype.

🎯 Exam Tip: Clearly distinguish between phenotypic and genotypic ratios, especially in monohybrid and dihybrid crosses, as they are rarely identical.

Question 10.
Phenotype means the pairs of genes responsible for the visible characteristics of organisms.
Answer: False. Phentotype means external appearance of visible characteristics of organisms.
In simple words: Phenotype refers to the observable physical or biochemical characteristics of an organism, while genotype refers to its genetic constitution.

🎯 Exam Tip: Master the definitions of 'phenotype' (what you see) and 'genotype' (the genetic code) as they are core to genetics.

Question 11.
During gamete formation, in Pj generation the pair of gametes separate independently.
Answer: True
In simple words: This statement refers to Mendel's Law of Segregation, where allele pairs separate during gamete formation, ensuring each gamete receives only one allele from the pair.

🎯 Exam Tip: Understand Mendel's Laws of Segregation and Independent Assortment as they describe how genetic traits are passed down.

Question 12.
Down syndrome is caused due to monosomy of X chromosome.
Answer: False. Down syndrome is caused due to trisomy of 21st chromosome.
In simple words: Down syndrome is caused by the presence of an extra copy of chromosome 21 (trisomy 21), not related to sex chromosomes.

🎯 Exam Tip: Accurately identify the chromosomal abnormality associated with Down syndrome (trisomy 21).

Question 13.
In Klinefelter syndrome, women are sterile.
Answer: False. In Klinefelter syndrome, men are sterile as this disorder arises in men due to abnormality in sex chromosome.
In simple words: Klinefelter syndrome affects males, characterized by an extra X chromosome (XXY), leading to sterility and other developmental issues.

🎯 Exam Tip: Correctly associate Klinefelter syndrome with males and Turner syndrome with females when discussing sex chromosome abnormalities.

Question 14.
If the father and mother are both sufferers or carriers of sickle-cell anaemia, their offsprings are likely to suffer from this disease.
Answer: True
In simple words: If both parents are carriers (AS) or sufferers (SS), there is a significant probability that their children will inherit two recessive alleles and develop sickle-cell anaemia.

🎯 Exam Tip: Emphasize the importance of genetic counseling for hereditary diseases when both parents are carriers or affected.

Question 15.
During fertilization, mitochondria is contributed by the sperm cell and egg cell(ovum).
Answer: False. During fertilization, mitochondria is contributed by the egg cell (ovum) alone.
In simple words: Mitochondria are exclusively inherited from the mother through the egg cell, as the sperm contributes negligible mitochondria to the zygote.

🎯 Exam Tip: Understand maternal inheritance of mitochondria, a key concept for mitochondrial disorders.

Question 16.
Polygenic disorders strictly follow Mendel's principles of heredity.
Answer: False. Polygenic disorders do not strictly follow Mendel's principles of heredity.
In simple words: Polygenic disorders are influenced by multiple genes and often environmental factors, making their inheritance patterns more complex and not strictly adhering to simple Mendelian ratios.

🎯 Exam Tip: Differentiate between simple Mendelian inheritance (single gene) and complex polygenic inheritance (multiple genes, environmental factors).

Question 17.
Genetic material is transferred in equal quantity from parents to progeny.
Answer: True
In simple words: During sexual reproduction, each parent contributes half of their genetic material (via gametes) to the offspring, ensuring an equal quantity of genetic information from both sides.

🎯 Exam Tip: This statement highlights the fundamental principle of equal parental contribution to offspring's genetic makeup in sexually reproducing organisms.

Give Scientific Reasons:

Question 1.
DNA molecules are called as 'Master molecules'.
Answer:
• Molecules of DNA are present in all organisms from viruses and bacteria to human beings.
• These molecules control the functioning, growth and division (reproduction) of the cell.
• Genes present in the DNA are also responsible for transfer of hereditary characteristics from parents to offsprings.
• Therefore, DNA molecules are called as 'Master molecules'.
In simple words: DNA is called the 'Master molecule' because it holds all the genetic instructions for an organism, controlling cell functions, growth, reproduction, and the inheritance of traits.

🎯 Exam Tip: Emphasize DNA's role in storing genetic information, controlling cell activities, and heredity when explaining why it's a 'master molecule'.

Question 2.
Phenotypic and genotypic ratios are different.
Answer:
• Phenotype means external appearance or visible characteristics of organisms whereas the genotype is the pairs of genes responsible for the visible characteristics.
• The genes responsible for any particular character are present in pairs.
• Though, there are two genes, the phenotype
depends on the presence of the dominant gene, e.g. Genotype for tall height of the plant is TT or Tt.
• Therefore, phenotypic and genotypic ratios are different.
In simple words: Phenotypic ratios reflect observable traits, while genotypic ratios represent the actual genetic composition. They differ because dominant alleles mask recessive ones, meaning multiple genotypes can express the same phenotype.

🎯 Exam Tip: Explain the concepts of dominance and recessiveness as the core reason for the divergence between phenotypic and genotypic ratios.

Question 3.
A carrier or sufferer of sickle-cell anaemia should avoid marriage with another carrier or sufferer.
Answer:
• Sickle-cell anaemia is a hereditary disease caused due to mutation of a single gene.
• It is a monogenic disorder that occurs due to changes in a gene during conception.
• If father and mother both are sufferers or carriers of sickle-cell anaemia, their offsprings are likely to suffer from the disease.
• Therefore, a carrier or sufferer of sickle-cell anaemia should avoid marriage with another carrier or sufferer.
In simple words: Individuals with sickle-cell anaemia or those who are carriers should avoid marrying another carrier or sufferer to prevent the high risk of their children inheriting the full-blown disease.

🎯 Exam Tip: Highlight the importance of genetic counseling for hereditary disorders to inform reproductive decisions and minimize disease transmission.

Question 3.
Mitochondrial disorders are inherited from the mother only.
Answer:
• Mitochondrial DNA becomes defective due to mutation.
• During fertilization, mitochondria are contributed by the egg cell (ovum) alone.
• Hence, mitochondrial disorders are inherited from the mother only.
In simple words: Mitochondrial disorders are passed down exclusively from the mother because only the egg cell contributes mitochondria to the developing embryo during fertilization.

🎯 Exam Tip: Explain that paternal mitochondria are typically eliminated or do not contribute to the zygote, ensuring maternal inheritance of mitochondrial traits.

Question 4.
Tobacco smoking causes cancer.
Answer:
• Tobacco smoke contains harmful chemicals like pyridine, ammonia, aldehyde furfural, carbon monoxide, nicotine, sulphur dioxide etc.
• They cause uncontrolled cell division.
• Tobacco smoke is full of minute carbon particles which cause normal tissue lining of the lung to transform into thickened black tissue. This leads to cancer.
• Therefore, tobacco smoking causes cancer.
In simple words: Tobacco smoke contains numerous carcinogens that damage DNA and promote uncontrolled cell division, leading to the development of cancer, especially in the lungs and other related organs.

🎯 Exam Tip: When discussing cancer, link environmental factors like tobacco smoking to cellular mechanisms, specifically uncontrolled cell division and DNA damage.

Define The Following Terms:

Question 1.
Gene
Answer: The segment of DNA which contains all the information for synthesis of a particular protein is called a 'gene'.
In simple words: A gene is a specific section of DNA that carries the instructions to build a particular protein, thus controlling a specific trait.

🎯 Exam Tip: Define 'gene' as the fundamental unit of heredity, a segment of DNA encoding for a specific product, usually a protein.

Question 2.
Chromosome
Answer: The structure in the nucleus of the cells that carries the hereditary characteristics is called chromosome.
In simple words: A chromosome is a thread-like structure located inside the nucleus of animal and plant cells, made of DNA and protein, carrying genetic information in the form of genes.

🎯 Exam Tip: Emphasize that chromosomes are the organized structures within the nucleus where genetic material (DNA) is stored and transmitted.

Question 3.
Genetics
Answer: The branch of biology which studies the transfer of characteristics of organism from one generation to the next and genes in particular, is called genetics.
In simple words: Genetics is the scientific study of heredity, focusing on how traits are passed from parents to offspring, and the structure and function of genes.

🎯 Exam Tip: Use 'heredity' and 'genes' as keywords when defining genetics to capture its core focus.

Question 4.
Heredity
Answer: Transfer of characteristics from parents to offsprings is called heredity.
In simple words: Heredity is the process by which genetic information and traits are passed down from parents to their biological children.

🎯 Exam Tip: Keep the definition of heredity concise and focused on the transmission of traits across generations.

Question 5.
Homologous chromosomes
Answer: If the pair consists of chromosomes are similar in shape and organization, they are called homologous chromosomes.
In simple words: Homologous chromosomes are pairs of chromosomes, one inherited from each parent, that are similar in length, gene position, and centromere location.

🎯 Exam Tip: Stress that homologous chromosomes carry genes for the same traits at the same loci, even if they have different alleles.

Question 6.
Heterologous chromosomes
Answer: If the pair which consists of chromosomes are not similar in shape and organization, they are called heterologous chromosomes.
In simple words: Heterologous chromosomes are chromosomes that do not pair during meiosis and differ in size, shape, and genetic content, like the X and Y sex chromosomes.

🎯 Exam Tip: Use the example of X and Y chromosomes to illustrate heterologous chromosomes, highlighting their difference in genetic content.

Question 7.
Genetic disorders
Answer: Diseases or disorders occuring due to abnormalities in chromosomes and mutations in genes are called genetic disorders.
In simple words: Genetic disorders are health conditions caused by abnormalities in an individual's DNA, ranging from single gene mutations to chromosomal changes.

🎯 Exam Tip: Clearly link genetic disorders to defects in either genes (mutations) or chromosomes (abnormalities in number or structure).

Distinguish Between:

Question 1.
DNA and RNA
Answer:

DNA	RNA
(i) In DNA, the sugar present is deoxyribose.	(i) In RNA, the sugar present is ribose.
(ii) In DNA, the nitrogen bases are adenine, guanine, cytosine and thymine.	(ii) In RNA, the nitrogen base thymine is replaced by uracil.
(iii) DNA is double stranded.	(iii) RNA is single-stranded.
(iv) DNA carries hereditary information	(iv) RNA helps in protein synthesis.

In simple words: DNA stores genetic information as a double helix with deoxyribose sugar and thymine, while RNA helps express that information as a single strand with ribose sugar and uracil.

🎯 Exam Tip: Focus on key differences: sugar type (deoxyribose vs. ribose), nitrogenous bases (thymine vs. uracil), and strandedness (double vs. single).

Question 2.
Turner syndrome and Klinefelter syndrome.
Answer:

Turner syndrome	Kline fater syndrome
(i) It is due to monosomy of sex chromosome.	(i) It is due to felter of sex chromosome.
(ii) Disorder in sex chromosome results in 44 + X condition.	(ii) Disorder in sex chromosome results is 44 + XY condition.
(iii) Seen in women.	(iii) Seen in men
(iv) Women suffering from this syndrome are sexually sterile.	(iv) Men suffering from this syndrome are sexually sterile.
(v) There is presence of total 45 chromosomes instead of 46.	(v) There is presence of total 47 chromosomes instead of 46.

In simple words: Turner syndrome affects females (45, X) causing sterility and a shorter stature, while Klinefelter syndrome affects males (47, XXY) leading to sterility and reduced secondary sexual characteristics.

🎯 Exam Tip: Clearly state the affected sex, the specific chromosomal abnormality (karyotype), and common phenotypic features for each syndrome.

 

Write Short Notes On:

Question 1. Albinism
Answer:

• Albinism is a monogenic disorder.
• Our eyes, skin and hair have colour due to the brown pigment melanin. In this disease, the body cannot produce melanin.
• The skin becomes pale, hair are white and eyes are usually pink due to absence of melanin pigment in the retina and sclera.

In simple words: Albinism is a genetic disorder where the body cannot produce melanin, leading to pale skin, white hair, and pink eyes. It's inherited through a single gene mutation.

🎯 Exam Tip: Focus on identifying albinism as a monogenic disorder and its primary symptom, which is the absence of melanin pigment.

 

Question 2. Polygenic disorders.
Answer:

• Polygenic disorders are caused due to mutations in more than one gene.
• In most such cases, their severity increases due to effects of environmental factors on the foetus.'
• Common examples of such disorders are cleft lip, cleft palate, constricted stomach, spina bifida (a defect of the spinal cord), etc. Besides diabetes, blood pressure, heart disorders, asthma and obesity are also polygenic disorders.
• Polygenic disorders do not strictly follow Mendel's principles of heredity.
• These disorders arise from a complex interaction between environment, life style and defects in several genes.

In simple words: Polygenic disorders result from mutations in multiple genes, often influenced by environmental factors, and do not follow simple Mendelian inheritance patterns. Examples include diabetes and heart disorders.

🎯 Exam Tip: Remember that polygenic disorders involve multiple genes and environmental factors, distinguishing them from monogenic disorders.

 

Question 3. Turner syndrome.
Answer:

• Turner syndrome is a disorder arising in women due to abnormality in sex chromosomes.
• Turner syndrome arises due to either inheritance of only one X chromosome from parents or due to inactivation of the gender- related part of X-chromosomes.
• Instead of the normal 44 + XX condition, women suffering from Turner syndrome show a 44 + X condition.
• Such women are sterile i.e. unable to have children due to improper growth of the reproductive organ.

In simple words: Turner syndrome is a chromosomal disorder in women where they have only one X chromosome (44 + X), leading to sterility and underdeveloped reproductive organs.

🎯 Exam Tip: Key points for Turner syndrome are its occurrence in women, the 44 + X chromosomal condition, and the resulting sterility.

 

Answer The Following Questions:

Question 1. What are the main objectives of National Health Mission?
Answer:The main objectives of National Health Mission are:

• Strengthening of the rural and urban health facilities.
• Controlling various diseases and illnesses.
• Increasing public awareness about health.
• Offering financial assistance to patients through various schemes.

In simple words: The National Health Mission aims to improve healthcare in both rural and urban areas, control diseases, raise health awareness, and provide financial aid for patient care.

🎯 Exam Tip: List at least three distinct objectives of the National Health Mission, focusing on accessibility, disease control, and public awareness.

 

Question 2. Which were the seven pairs of contrasting characteristics studied by Mendel in pea plant?
Answer:The seven pairs of contrasting characters studied by Mendel in pea plant were as follows:

Characters	Dominant	Recessive
Shape of the seed	Round(R)	Wrinkled (r)
Colour of the seed	Yellow (Y)	Green (y)
Colour of the flower	Purple (C)	White (c)
Shape of pod	Inflated (I)	Constricted (i)
Colour of pod	Green (G)	Yellow (g)
Position of flower	Axillary (A)	Terminal (a)
Height of the plant	Tall (T)	Dwarf (t)

In simple words: Mendel studied seven contrasting pairs of traits in pea plants, such as round vs. wrinkled seeds, yellow vs. green seeds, and tall vs. dwarf plants, to understand the principles of heredity.

🎯 Exam Tip: Be able to list at least four of Mendel's contrasting pea plant characteristics, specifying both the dominant and recessive forms.

 

Question 3. Name some dominant and recessive characteristics seen in human beings.
Answer:Some dominant and recessive characteristics of human beings.

Dominant	Recessive
Rolling tongue	Non-rolling tongue
Presence of hair on arms	Absence of hair on arms
Black and curly hair	Brown and straight hair
Free earlobe	Attached earlobe

In simple words: Humans exhibit various dominant and recessive traits, like tongue rolling (dominant) versus non-rolling (recessive), or free earlobes (dominant) versus attached earlobes (recessive).

🎯 Exam Tip: Provide at least two pairs of dominant and recessive human characteristics, such as tongue rolling and earlobe type.

 

Question 4. What is Klinefelter syndrome?
Answer:

• Klinefelter syndrome is a disorder arising in men due to abnormalities in sex chromosomes.
• In this disorder, men have one extra X chromosome, hence their chromosomal condition becomes 44 + XXY.
• Such men are usually sterile because their reproductive organs are not well developed.

In simple words: Klinefelter syndrome is a genetic condition affecting men who have an extra X chromosome (44 + XXY), typically leading to sterility and underdeveloped reproductive organs.

🎯 Exam Tip: For Klinefelter syndrome, remember it affects men, involves an extra X chromosome (XXY), and results in sterility.

 

Question 5. How is the diagnosis for sickle-cell anaemia made?
Answer:

• Under the National Health Mission scheme, the 'Solubility Test' for diagnosis of sickle-cell anaemia is available at all district hospitals.
• Similarly, the confirmatory diagnostic test - ‘Electrophoresis' is performed at rural and subdistrict hospitals.

In simple words: Sickle-cell anaemia is diagnosed through a Solubility Test at district hospitals and confirmed by Electrophoresis, especially in rural and subdistrict medical facilities.

🎯 Exam Tip: Name both the initial screening test (Solubility Test) and the confirmatory test (Electrophoresis) for sickle-cell anaemia diagnosis.

 

Question 6. Find out the Phenotypic ratio of the following:
(a) Round-Yellow
(b) Wrinkled-Yellow
(c) Round-Green
(d) Wrinkled-Green
Answer:
(a) Round-Yellow: 9
(b) Wrinkled-Yellow: 3
(c) Round-Green: 3
(d) Wrinkled-Green: 1
Phenotypic ratio: 9:3:3:1
In simple words: The phenotypic ratio 9:3:3:1 represents the four visible trait combinations from a dihybrid cross: 9 parts Round-Yellow, 3 parts Wrinkled-Yellow, 3 parts Round-Green, and 1 part Wrinkled-Green.

🎯 Exam Tip: This 9:3:3:1 ratio is a classic dihybrid cross phenotypic ratio; ensure you can associate each number with its respective phenotype.

 

Question 7. Find out the Genotypic ratio of the following:
(a) RRYY
(b) RRYy
(c) RRyy
(d) RrYY
(e) RrYy
(f) Rryy
(g) rrYY
(h) rrYy
(i) rryy
Answer:
(a) RRYY -1
(b) RRYy-2
(c) RRyy-1
(d) RrYY-2
(e) RrYy-4
(f) Rryy-2
(g) rrYY - 1
(h) rrYy - 2
(i) rryy - 1
Genotypic ratio: 1:2:1:2:4:2:1:2:1
In simple words: The genotypic ratio 1:2:1:2:4:2:1:2:1 details the frequency of each specific genetic combination (genotype) resulting from a dihybrid cross, showing the precise genetic makeup of the offspring.

🎯 Exam Tip: Understanding the complex genotypic ratio (1:2:1:2:4:2:1:2:1) is crucial for dihybrid crosses; practice associating each numerical value with its specific genotype.

 

Draw Neat And Labelled Diagrams Of The Following:

Question 1. Structure of chromosome
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): एक गुणसूत्र की संरचना को दर्शाया गया है जिसमें पी-आर्म, क्यू-आर्म, सेंट्रोमीयर और डीएनए शामिल हैं। यह एक एक्स-आकार की संरचना है जहाँ सेंट्रोमीयर दो क्रोमेटिड को जोड़ता है।
In simple words: A chromosome consists of two chromatids joined at the centromere, with distinct p-arms and q-arms, and is primarily composed of DNA.

🎯 Exam Tip: When drawing a chromosome, accurately label the centromere, p-arm, q-arm, and indicate the presence of DNA for full marks.

 

Question 2. Types of RNA
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र आरएनए के विभिन्न प्रकारों - मैसेंजर आरएनए (mRNA), राइबोसोमल आरएनए (rRNA) और ट्रांसफर आरएनए (tRNA) की आकृतियों को दर्शाता है। mRNA एक लंबी सीधी श्रृंखला है, rRNA एक अधिक जटिल, मुड़ी हुई संरचना है, और tRNA एक क्लोवर पत्ती जैसी संरचना है।
In simple words: The three main types of RNA are messenger RNA (mRNA) which carries genetic instructions, ribosomal RNA (rRNA) which forms ribosomes, and transfer RNA (tRNA) which transports amino acids.

🎯 Exam Tip: Be able to identify and briefly describe the distinct shapes and primary functions of mRNA, rRNA, and tRNA.

 

Answer The Following Questions:

Question 1. What are the effects of tobacco consumption?
Answer:

• Smoking of cigarettes and bidis adversely affects the process of digestion.
• It causes a burning sensation in the throat and cough.
• Excessive smoking causes instability and trembling of fingers.
• It causes dry cough which leads to sleeplessness.
• Tobacco consumption can lead to shortening of life span, chronic bronchitis, pericarditis, cancer of the lungs, mouth, larynx (voice box), pharynx, urinary bladder, lips or tongue.
• The nicotine present in tobacco affects the central and peripheral nervous system. Arteries become hard i.e. it causes arteriosclerosis and hypertension.

In simple words: Tobacco consumption causes severe health issues like digestive problems, chronic respiratory diseases, various cancers (lungs, mouth), and cardiovascular problems like arteriosclerosis and hypertension.

🎯 Exam Tip: List at least five adverse effects of tobacco consumption, covering different body systems such as respiratory, digestive, and circulatory, and common cancers.

 

Question 2. Complete the table for number of chromosomes in different organisms.
Answer:

Organism	No. of Chromosomes
Crab	200
Maize	20
Frog	26
Roundworm	04
Potato	48
Human	46
Dog	78
Elephant	56
Fruit fly	08
Mango	40

In simple words: The number of chromosomes varies significantly across different organisms, for example, humans have 46, maize has 20, and crabs have 200, highlighting the diversity in genetic composition.

🎯 Exam Tip: Memorize the chromosome numbers for commonly cited organisms like humans, fruit flies, and maize, as they are often used in genetics examples.